From the discusison I had with a Diff guy last year, the whole housing will need to change. A 3.45 gear set has a different diameter to the 2.77 set so you cant just bolt the gears on. Thats what they told me anyway...

Heaps of 2nd hand diffs in the Quokka. You can pick them up pretty cheap from there. Got a 2.92 lsd out of an EA, complete with disks, calipers for $100 AU.
Some time ago saw a 3.45 out of an XR6 for $300 AU. Didn't have the money, else it would be under the XF now. Maybe next time. Just got to keep looking when i get some spare $$$$$$.

You will find 3.23 under 3 speel manual ute and panelvans. I noticed alot from going to a 3.23. Good value.
A 3.45 out of a XR6 or XR8 will fit. you have to use the XF gear cover though. 3.23 will bolt straight up, no probs.
I cleaned mine, painted it gloss black and replaced the oil. Not 'cause I had to but I wanted too.